Electrocautery surgical instruments are used to make surgical cuts and to coagulate blood along surgical cuts and around surgical sites. Electrocautery surgical instruments typically have an exposed electrode blade positioned on the lower end of an elongated body. The elongated body fits comfortably in the hand of a surgeon, and allows the surgeon to control and manipulate the electrode blade much in the manner of a conventional metal scalpel. An electric cable or cord extends from the non-cutting upper end of the elongated body. One end of the electrical cord is electrically coupled to the electrode blade, while the other end of the cord is electrically coupled to a commercially available electrosurgical generator.
Electrosurgical generators have a radio frequency oscillator circuit which delivers highvoltage, high-frequency electrical signals of various waveforms to the electrode blade to selectively sever, clamp or coagulate tissue during surgical procedures. The electrosurgical generator converts wall current (110 V, 60 Hz) into high-frequency radio waves in the range of 500,000 to 1,000,00 Hz. Electrosurgical generators typically generate two or three types ofradio frequency waves. One wave is a dampened sine wave with pure coagulating properties. Another wave is a sinusoidal wave form that has pure cutting properties. Electrosurgical generators can also generate a variable sine wave with ablended current that combines characteristics of the dampened sinusoidal and sinusoidal waves. The dampened sine wave has excellent coagulating properties, but results in marked tissue destruction and charring. The sinusoidal wave cuts through tissue with little thermal damage, much like a conventional scalpel, but has no coagulation properties. Most surgical dissection is performed with a dampened sine wave output that cuts and coagulates simultaneously with minimal thermal destruction and charring. The selection of the particular type of waveform can be regulated by a foot control pedal associated with the electrosurgical generator, or by finger controls mounted on the electrosurgical instrument. See e.g. U.S. Pat. No. 5,318,565 (Kuriloff).
Most systems for supplying the current to the electrode blade utilize a dispersive, or indifferent, electrode. The dispersive electrode is typically a large metal plate which is secured to the patient and is electrically coupled to the electrosurgical generator through a cable. The electrode blade serves as an active electrode. The high frequency current produced by the electrosurgical generator radiates from the site of tissue contact of the active electrode/electrode blade, through the tissues of the patient to the larger indifferent electrode, back to the power oscillator of the electrosurgical generator, and then back again to the site of tissue contact of the electrode blade, in a continuing radiating cycle. The current reaches a high density at the site where the electrode blade contacts the tissue, producing cutting or coagulation. The dispersive electrode is relatively large in area, which keeps current density in the region of the dispersive electrode sufficiently low to avoid tissue burns in the patient, except where the electrode blade contacts tissue.
U.S. Pat. Nos. 4,919,129 (Weber) and 5,035,695 (Weber) disclose electrocautery surgical instruments having apartially retractable electrode blade. The surgical instruments include attachable extension units of varying lengths for selectively extending the operational utility of the instrument as a surgical procedure progresses. The extension units extend the electrode blade a selected dimension to facilitate deep surgical procedures in confined sites. A safety switch is included for controlling the application of high-voltage electrical signals to the electrode blade, and to thereby establish electrically inactive conditions during attachment and removal of extension units.
The present invention utilizes the above concepts, but applies them in a surgical apparatus which is adjustable in length through a wide range of motion.